In vehicles, there is a hybrid vehicle equipped with an internal combustion engine and a motor generator as a drive source. In this hybrid vehicle, the engine is directly connected to the motor generator that performs the function of driving and assisting the engine. The states of the driving and assisting by the motor are controlled according to the driving states of the hybrid vehicle and the engine. Also, in a conventional controller for the hybrid vehicle, the hybrid vehicle is equipped with a motor generator (referred to as “motor”) as well as the engine to improve fuel economy. This type of arrangement is disclosed in JP Patent Number 3350465 and JP Application Laid-Open No. H08-317506.
Conventionally, the quantity of electric power generated by the motor is determined based on the engine speed, i.e., the quantity of generated electric power decreases with decreasing engine speed and is set to become zero when the engine speed is below a speed for canceling fuel cut (return speed).
In this system, the regenerative braking torque does not interfere with the engine torque when a fuel supply controller restarts fuel supply. Accordingly, engine stall is prevented to eliminate a driver's worry that engine stop will occur in opposition to the driver's intent. Therefore comfortable driving of the vehicle is maintained.
Also, in this system, the quantity of electric power generation gradually decreases to zero in accordance with the engine speed decreasing from a certain threshold speed to a return speed. This avoids an unexpected shock to a passenger or operator which may result from sudden prevention of generation during deceleration when the fuel supply controller restarts fuel supply. Thus, comfortable driving of the vehicle can be achieved.
However, the quantity of power generation is based on the engine speed even after the fuel cut is cancelled, and the power generation is therefore reduced to and maintained in a quantity or amount that prevents engine stall. After the fuel cut is canceled, the power generation decreases more than needed, and power generation that should ordinarily be collected is not collected.
In particular, for a vehicle provided with an automatic transmission with a torque converter, the quantity of air for idle in a running range is set at more than that in a non-running range to increase the engine output torque so as to prevent engine stall due to an increase of creep torque load. During coasting, the engine speed is greater than needed in comparison with the engine speed at idling due to the force from the drive wheels. Thus fuel economy is decreased.